Honu, Y. A. K. and D. J. Gibson (Southern Illinois University at Carbondale, Department of Plant Biology, Center for Ecology, 1125 Lincoln Drive, Carbondale, Illinois 62901-6509, USA). Microhabitat factors and the distribution of exotic species across forest edges in temperate deciduous forest of southern Illinois, USA. J. Torrey Bot. Soc. 133(2): 255–266. 2006.—The study of microhabitat factors has attracted the attention of ecologists for about half a century. We examined crop-forest, access road-forest, and hay field-forest edge types in temperate deciduous forest in Southern Illinois to obtain information that may contribute to the control and management of exotic species. Forest edges have different abiotic factors compared to the interior, a phenomenon known as an edge effect. To investigate microhabitat factors, three 90 m transects were established from the forest boundary into the interior at each of the three edges in July 2002. Twelve 3.14 m² circular plots at 5 m intervals from each other for the first 20 m and 10 m apart thereafter were established along each transect. A 550 cm³ soil core was extracted from the six cm A-horizon in each plot along the three transects in August 2002 and analyzed for soil texture, pH., and major soil nutrients. To quantify the edge effect, the Distance of Edge Influence (DEI) was calculated by contrasting the value of microhabitat factors in plots ≤ 50 m from the forest boundary with the value of microhabitat factors in plots > 50 m from the boundary (interior plots) using a permutation approach. The DEI is calculated as the distance where two or more consecutive plots from the forest boundary have values that differ significantly from the expected value of the interior plots. Percent clay and sand generally declined across the crop-forest and access road-forest edges into the interior while the opposite relationship was observed at the hay field-forest edge. Percent silt showed a pattern that was opposite to those exhibited by percent sand and clay at all the three edge types. The DEI of the percent sand, clay, and silt varied between 15 to 50 m at the three edges. Seven exotic species were present in the vegetation and the relationship of the abundance of three of them to 11 microhabitat factors was tested. Lonicera japonica and Allium vineale were absent when canopy openness was < 15 % while the presence of Cardamine hirsuta was independent of canopy openness. Management strategies for the control of the invasive L. japonica and A. vineale should consider canopy closure among other factors. By contrast, management prescriptions for the exotic C. hirsuta may pose a challenge to forest managers and conservation biologists as a result of its insensitiveness to the 11 microhabitat factors including light (canopy openness) measured in this study. For conservation purposes, a buffer strip of 50 m around a conservation area would eliminate most of these microhabitat edge effects.